Speaking about his decision for the first time publicly, Ricciardo said on a video blog: "It was by far the toughest decision I've made in my racing career but in 29 years living on this Earth, it was actually one of the toughest life decisions I've made.

"I felt it was a time now where it was good for me to move on and have a fresh start somewhere else. I think it will be healthy for me - so excited for what lies ahead with Renault."

The deal that nobody saw comingRicciardo had been expected to re-commit to Red Bull after Mercedes re-signed Lewis Hamilton and Valtteri Bottas for 2019 while Charles Leclerc is the overwhelming favourite to replace Kimi Raikkonen at Ferrari if the Finn isn't retained.

"Not every door has closed but it is looking more and more likely that the other [top] teams will remain with their line-ups," Ricciardo said at the British GP. "If it wasn't Red Bull, they [Mercedes and Ferrari] are the two most attractive options. So if they are not possible it's hard for me to be convinced there is a better option than Red Bull."

Although McLaren, who believe they were "pretty close" to signing Ricciardo after offering the 29-year-old a sizeable pay rise, Renault were thought to be no more than an outside option for the Australian.

Ricciardo's own public pronouncements had also strongly indicated he was set to re-sign with Red Bull. Having said at Silverstone "it is obviously looking more and more likely I will remain", Ricciardo told reporters as recently as Wednesday after testing in Hungary: "It will definitely be done by Spa."

The 'it', however, turned out to be something very different.

According to reports, Christian Horner was so surprised by Ricciardo's decision the Red Bull boss initially thought his driver was joking when Ricciardo phoned on Thursday night to inform him he was switching to Renault - Red Bull's long-time engine suppliers but who have been dropped for 2019.

Renault’s Abiteboul may brag about wrong-footing Horner, but essentially Ricciardo just wanted a change, something Horner never really took seriously.. https://t.co/bXJlgpXw8u

Will Ricciardo's gamble prove a good move?Sky F1's Martin Brundle has described Ricciardo's switch as a "bold" move and "a bigger risk" than the gamble Lewis Hamilton took in 2012 when he decided to leave McLaren for Mercedes.

But in quotes attributed to him by Renault, Ricciardo said: "I realise there is a lot ahead in order to allow Renault to reach their target of competing at the highest level but I have been impressed by their progression in only two years, and I know each time Renault has been in the sport they eventually won."

What now for the F1 transfer market?Ricciardo's shock decision to quit Red Bull for Renault - where he will partner Nico Hulkenberg in 2019 - will have immediate and unexpected repercussions in the F1 driver market.

If he doesn't return to parent team Red Bull as a replacement for Ricciardo, Carlos Sainz is expected to join McLaren.

If @Carlossainz55 doesn’t get a strong drive in F1 next year it will be a travesty, annoy me intensely, and reflect badly on F1.

But Riccardo's transfer to Renault scuppers expectations Esteban Ocon was on the cusp of moving to the French team for 2019 from Force India.

And that, in turn, has seemingly put a block on predictions Lance Stroll will leave Williams for Force India at the end of 2018 - although that could still happen if, as suggested, Sergio Perez leaves Force India (Full story - read more).

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